How to retrieve a response from server for the request sent?

Question

I am developing an application that connects to a remote web server and exchanges data with the web server frequently. First screen of my application provides login screen that authenticates user.

I am able to authenticate user on the web server by sending a request to the server but unable to get response from the server to display success alert to the user on the iphone. In clear, I am not getting any response.

The server I'm using is developed in Java.

I am using the following to send the request to server.

NSString *post = @"username=";

post = [post stringByAppendingString:username];
post = [post stringByAppendingString:@"&password="];
post = [post stringByAppendingString:password];

NSData *postData = [post dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES];

NSString *postLength = [NSString stringWithFormat:@"%d", [postData length]];

NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];
[request setURL:[NSURL URLWithString:@"http://example.com/login.action?"]];
[request setHTTPMethod:@"POST"];
[request setValue:postLength forHTTPHeaderField:@"Content-Length"];
[request setHTTPBody:postData];
NSURLConnection *conn=[[NSURLConnection alloc] initWithRequest:request delegate:self];

And,

- (void)connectionNSURLConnection *)connection didReceiveDataNSData *)data
{
[receivedData appendData:data];
NSString *ReturnStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(@"In \"didReceiveData()\" : receivedData = %@",receivedData);
NSLog(@"Return String : %@", ReturnStr);

}

This function is never called.

What should I do to receive response for the request I have sent?

A brief collection of my queries:

Example: Login screen that validates a user in Java server

1. I am sending request that I am able to see at the console of my server application.
2. I'm unable to get response for the request.
3. In which format the response data must be sent?

Would someone provide a clear picture of data exchange between the iPhone application and a Java servlet?

Update

I have implemented these three methods also. But no response from server. Can you guide me the process of developing LOGIN application that communicates with a JAVA server by requests and responses? I am stuck with communicating.

Yeah, my server is receiving request from iphone. I am able to see the request that is sent to the server.

I am not able to understand how the data exchange between iphone application and JAVA server takes place. I'm a newbie to this iphone development.

Answer 1

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    [responseData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSString *failureMessage = [NSString stringWithFormat:@"Connection failed: %@", [error description]];
    NSLog(failureMessage);

}

Try implementing these three methods as well, you might be getting an error or no response. You can tell by using these methods.

Answer 2

you should verify that the server is actually recieving the request from the iphone. a simple php script should return something.

<?php

    echo print_r($_GET, true);
    echo print_r($_POST, true);
?>

create a dummy app that makes a request to the script and displays the response

Answer 3

I'm not sure what authentication you refer to with LOGIN, but if the server requires HTTP Auth, you need to implement the delegate method

- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge;

Answer 4

I am using the following to send the request to server.

The code looks OK, but where is this code and what happens before and after the code you've shown us? Is it in a handler for a button press? Is it in a background thread?

For the asynchronous load you are using to work properly, you need to be on a thread with a default run loop, e.g. the main thread. And this code must return control to the run loop, i.e. must not busy wait doing something else.

Another thing to check is your server - is it in fact sending a response? If you send the same request from a browser, what content length do you get back?

Edit: it may help if you also show the java action handler on the server side. For example, does it send a HTTP redirect if the login is successful? And are you implementing the following delegate method:

- (NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse

...and if so, what does that method look like. I'm wondering if you've maybe implemented this method and not got the right logic in there, thus stopped a redirect from happening.

Answer 5

U can do it this way...

-(NSString* )createWebServiveRequest:(NSString *)urlLink{
   NSURL *url = [NSURL URLWithString:urlLink];
   NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:60];
   NSData *returnData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse: nil error: nil ];
   NSString *responseString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];
   return responseString;
}

call the above method with the NSString containing url.....and capture it in the method call.